Selective Oxidation of sp-Bonded Carbon in Graphdiyne/Carbon Nanotubes Heterostructures to Form Dominant Epoxy Groups for Two-Electron Oxygen Reduction.

Two-electron oxygen reduction reaction (2e ORR) is of great significance to HO production and reversible nonalkaline Zn-air batteries (ZABs). Multiple oxygen-containing sp-bonded nanocarbons have been developed as electrocatalysts for 2e ORR, but they still suffer from poor activity and stability due to the limited and mixed active sites at the edges as well as hydrophilic character. Herein, graphdiyne (GDY) with rich sp-C bonds is studied for enhanced 2e ORR. First, computational studies show that GDY has a favorable formation energy for producing five-membered epoxy ring-dominated groups, which is selective toward the 2e ORR pathway. Then based on the difference in chemical activity of sp-C bonds in GDY and sp-C bonds in CNTs, we experimentally achieved conductive and hydrophobic carbon nanotubes (CNTs) covering O-modified GDY (CNTs/GDY-O) through a mild oxidation treatment combined with an in situ CNTs growth approach. Consequently, the CNTs/GDY-O exhibits an average Faraday efficiency of 91.8% toward HO production and record stability over 330 h in neutral media. As a cathode electrocatalyst, it greatly extends the lifetime of 2e nonalkaline ZABs at both room and subzero temperatures.